Cornwall Mammal Group

Order: Rodentia

Recognition:

The harvest mouse is Europe’s smallest rodent, weighing only 4 to 6 g (less than a 2p coin!) and measuring only 50 to 70 mm in
length. Their small size is reflected in their Latin name ‘Micromys minutus’ derived from the Greek micros (small), mys (mouse) and the Latin minutus (tiny). Tiny small mouse! This agile little animal lives among stiff
vegetation and is small enough to curl up on a teasel and to climb among the seed heads of a grain crop. Although often feeding among arable crops, most harvest mice live in the hedges and margins of the fields where they are less likely to be disturbed by agricultural machinery. They have a reddish/ yellow coat with a white underside. They have hairy ears, and they have a blunter nose compared with the wood mouse or house mouse. The tail is as long as the head and body together and the animal uses its tail to grip grass stalks while climbing.

The harvest mouse was first described in 1767 by the naturalist Gilbert White. He

noted, 'they never enter houses; are carried into ricks and barns with ye sheaves, and abound in harvest'. They are traditionally associated with arable fields, but recent
research shows that their main requirement is tall, dense vegetation and they live in a
range of habitats including reed beds, roadside verges, open grassland and hedgerows.

Harvest mice have very high energy requirements, searching throughout the day

amongst the stalks of long grasses and reeds for seeds, berries and small insects. They are most active around dawn and dusk. In winter, as the vegetation dies back, they
spend more time foraging at ground level.

Harvest mice usually have two or three litters a year between late May and October,

most being between August and September. There are usually around six young in a litter, which are born in carefully woven grass nests, roughly the size of a tennis ball. The pups weigh only about 0.6 g at birth, but at 2 weeks the mother leaves them to their own devices and heads off to set up a new nest. In the winter harvest mice descend to ground level and use food stores to survive until the spring.

Harvest mice have many predators including weasels, stoats, foxes, cats, owls, hawks, crows and even pheasants. Harvest mice are also vulnerable in low temperatures and can die from cold and starvation in harsh winters; mice rarely live longer than a year, although in captivity some animals have lived to 5 years.

The major evidence of the presence of this tiny animal is the nest, woven from shredded living grass and tightly wound
into the stems of cereals, tussocks, herbs or brambles, built between 300 mm and 1m above ground level. Breeding nests are about 100 mm in diameter, non-breeding nests are smaller. Each animal may build
several nests through the year and they

The harvest mouse is widespread across Cornwall but poorly recorded. There are no records from the Isles of Scilly. Harvest mice are locally common, but thought to be declining due to changes in agricultural methods. They are more common in the south and east of the UK than more northerly areas and are absent from Ireland. The harvest
mouse occurs across Europe, except the Iberian peninsular, through Asia to northern India.

Records:

2007-2012: 37

2002-2007: 81

Pre-2001: 136

Total: 254

Cornish Tales:

A recent site for harvest mice in North Cornwall was recorded when electric fences were being moved on a dairy farm. Harvest mice nests were found among the kale which was being used as a fodder crop.

Did you know?:

The harvest mouse is the only old world mammal to have a truly prehensile tail,
which it uses to grasp vegetation. Harvest mice shred grass by pulling it through
their teeth and then use the shredded grass to weave their distinctive nests.

Conservation:

Harvest mice are not legally protected in Britain but the species was recently
classified as a UK Biodiversity Action Plan priority species in recognition of their
declining numbers.